SVG-ACTION-3703: Change embedded content chapter to allow these things from resolution: allow html nsed elements audio, video, canvas, iframe in an svg subtree as a child of a container element with the containing block being the nearest svg viewport and blockyfied

SVG-ACTION-3739: Add a new keyword value to the x and y properties that means use-the-list-of-lengths in the attributes, and set that with the ua stylesheet and add a note to say that it's still an open issue